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Photo-/Electrocatalytic Water Splitting

Materials Based on Graphene Transition Metal Compound Hybrids for Hydrogen Generation via Electrocatalysis

Two electrodes or two plates—typically made of a noble metal are submerged in water are connected to a DC electrical power source. At the cathode (where electrons enter the water), hydrogen will appear, and at the anode, oxygen. Assuming optimum faradaic efficiency, the amount of hydrogen and oxygen produced are both proportional to the overall electrical charge carried by the solution, with hydrogen being produced at a rate double that of oxygen. The use of an electrocatalyst and the addition of an electrolyte (such as salt, acid, or base) are critical to the process's viability.

Our current focus is on Development of Material based on Graphene Transition Metal Compounds Hybrids for Hydrogen Generation via Electrocatalysis. A potentially useful method for the mass manufacture of highly pure hydrogen is electrocatalysis, which is seen as the next generation of processes for producing fuel and power. Historically, catalysts made of metals like Pt, Ir, and Ru were employed in these processes. However, due to their low stability and expensive price, these precious metals cannot be used on an industrial scale. Therefore, we are concentrating on creating inexpensive catalysts that will eventually open the door for commercialization. Due to their extraordinary catalytic performance and plentiful reserves, transition metal compounds (transition metal oxides, phosphides, sulphides, nitrides, carbides, and selenides) are currently being explored as potential materials.

Photo and Photoelectrocatalytic Water Splitting by Visible Light using Up-conversion Material Incorporated Semiconductors

Production of photoexcited charge carriers serves as the foundation for the basic mechanism of photocatalysis water splitting. Three key steps are typically involved in the photocatalytic water splitting reaction on semiconductor particles: (1) absorption of photons with energies above that of semiconductor bandgap, (2) separation of the generated electrons and holes, and (3) migration of these charges to the interface of the semiconductor particles. Surface chemical reactions between these charge carriers available on photocatalyst interface result in the production of H2 and O2, respectively. Without taking part in any chemical reactions, recombination of electrons and holes is another possibility that might happen on a very short period.

Currently we are experimenting on photo and photoelectrocatalytic dissociation of water by visible light using up-conversion material incorporated semiconductors. Semiconductors with up-conversion (UC) effects have attracted considerable attention due to their ability to upconvert visible or near-infrared light to visible light, which can boost the activity of the photocatalysts and the utilisation of the sunlight. UC materials also open a new shortcut route for the development of the photocatalyst materials which could solve the problem that wide bandgap semiconductors have a narrow light response range.

Prototype Efficient Photoelectrochemical (PEC) Device for Hydrogen Generation

In the PEC system, hydrogen generation is a result of integrated solar energy conversion and water electrolysis in a single photocell. This procedure is considered to be a low-cost, renewable, and environmentally acceptable. In a typical PEC Cell reference electrode is typically included in the system to observe half reactions in the cell. The majority of this electrode arrangement is submerged in an aqueous electrolyte (Na2SO4). The Photoelectrochemical cell is either transparent to light or comprises an optical window that allows irradiation to reach the photoelectrode. n- or p-type semiconductor is often utilised as the working electrod. By photon absorption at an energy level equivalent to or greater than the bandgap (Eg) of the photoanode semiconductor, electron-hole pairs are produced. Electrons are gathered in the photoanode when an n-type semiconductor is employed, and they are then transferred to the counter electrode via an external circuit. As holes participate in the oxidation of water into O2 and H+ at the anode, photogenerated electrons are used to convert H+ into H2 at the cathode. In contrast, when a p-type semiconductor is used as the working electrode, water is oxidised into O2 and H+ in the counter electrode and H+ is reduced into H2 by photogenerated electrons.

While p-type semiconductors produce a cathodic photocurrent by sending electrons toward the electrolyte, n-type semiconductors produce an anodic photocurrent in which holes are transported toward the electrolyte. Major challenge in developing efficient PEC cells for water splitting relies on finding inexpensive materials that fulfil the requirements of an ideal photoelectrode e.g., (i) it has to have strong light absorption in the visible spectrum, (ii) high chemical stability in aqueous electrolyte solutions under dark and illuminated conditions, (iii) suitable band edge positions for hydrogen and oxygen evolutions, (iv) low kinetic overpotentials; and finally (v) the charge transfer at the semiconductor/electrolyte interface must be selective for water splitting or hydrogen generation.